Modern air conditioning and refrigeration systems provide cooling, ventilation, and humidity control for all or part of a climate controlled area such as a refrigerator, a cooler, a building, and the like. Generally described, a conventional refrigeration cycle includes four basic stages to provide cooling. First, a vapor refrigerant is compressed within one or more compressors at high pressure and high temperature. Second, the compressed vapor is cooled and condensed within a condenser by heat exchange with ambient air drawn or blown against a condenser coil. Third, the liquid refrigerant is passed through an expansion device that reduces both the pressure and the temperature. The liquid refrigerant is then pumped to one or more evaporators within the climate controlled area. The liquid refrigerant absorbs heat from the surrounding area in an evaporator coil and evaporates to a vapor. Finally, the vapor refrigerant returns to the compressor and the cycle repeats. Several alternatives to this basic refrigeration cycle are known and also may be used herein.
When the load on the overall refrigeration system is low, the compressor racks may be unloaded to match the low load. If the load, however, is lower than the minimum capacity output of the compressor rack, then the compressors may stop and start frequently. Such frequent action may cause damage to the compressors as well as disrupt the overall system oil return.